Looking for a new company to help run AMZN ads and account

The company I work for sells on amazon, and works with a company currently that helps us with all of our selling on amazon from: replenishment orders, refunds and discrepancies, ads, and basically there to help us run as effectively as possible. However they have not been working fast enough to our liking, and we want to look for a new company. Whats the best way to search out for a company to help with these things? Our current company is under the Amazon Partner Network, but I cant seem to find a list of Amazon Partner Companies to see what the other options are.